__author__ = 'wangleijie'
class parent:
    def callback(self, prefix, name, *param):
        method = getattr(self, prefix+name)
        if callable(method):
            return method(*param)
    def start(self, name):
        self.callback("start_", name)
    def overlaod(self):
        print "parent overload"
class child(parent):
    def start_url(self):
        print "url"
    def start_img(self):
        print "img"
    def overlaod(self):
        print "child overload"
        def overloadchild():
            print "overloadchild"
        overloadchild()

c = child();
c.start("url");
c.overlaod();